The present invention relates to a marine stern drive apparatus in which the engine is mounted within the boat and the drive unit mounted outside the boat. More particularly, the invention is directed to an improved system for selectively adjusting the lift and trim of the drive unit with respect to the boat transom.
Marine propulsion devices, including both outboard motors and stern drives, are typically supported from the boat transom by a drive mounting assembly. Various types of drive mounting assemblies are known, as for example a transom bracket used to mount an outboard motor directly on the boat transom or a gimbal ring assembly for mounting a stern drive unit directly to the transom. Typically, a drive unit mounted directly on a transom may be trimmed by pivoting it about a generally horizontal axis to position the propeller to optimize thrust with respect to the plane of the boat. However, the vertical position of the drive unit cannot typically be changed beyond the somewhat limited amount which results from the trimming operation. Therefore, the drive unit is generally mounted in a compromise position at an essentially fixed height which will provide the best overall performance.
Drive mounting assemblies have been developed which allow an outboard motor to be mounted aft of the boat transom in a manner which permits the motor to be either raised or lowered vertically with respect to the transom, as well as trimmed or tilted about a horizontal axis. Many of these transom extension types of outboard motor mounting assemblies are of a general type which includes a pivotally cited quadrilateral linkage. Such transom extension mounting assemblies have become increasingly popular on high performance boats where a lower motor position improves initial boat acceleration and a higher motor position enhances top speed by reducing gear case drag. Additionally, movement of an outboard motor vertically to a higher position reduces draft, thereby enhancing shallow water operation. It is also known that extending the mounting of an outboard motor aft of the transom improves the handling characteristics of many boats at high speeds.
U.S. Pat. No. 4,757,971 and U.S. patent applications Ser. No. 100,261, filed Sept. 23, 1987; Ser. No. 103,508, filed Oct. 1, 1987; and Ser. No. 181,685, filed Apr. 14, 1988, all of which are assigned to the assignee of this application, disclose outboard motor transom extension assemblies which utilize a quadrilateral linkage arrangement to raise and lower the motor with respect to the transom. The quadrilateral linkage comprises four pivotally connected links forming a collapsible linkage the movement of which effects vertical movement of the motor. If the collapsible linkage includes oppositely disposed links of equal length, collapse or opening of the linkage will cause a purely vertical movement of the motor. On the other hand, if either opposite pair of links are of unequal length, pivotal trimming or tilting movement of the motor will occur simultaneously with the vertical upward or downward movement.
In a marine stern drive unit, the engine is mounted inside the boat and the drive unit is attached to the outside of the transom. A fixed position drive shaft assembly interconnects the engine and the drive unit and provides for the transmission of power from the former to the latter. U.S. patent application Ser. No. 181,515, entitled "Variable Height Marine Propulsion Mechanism," filed Apr. 14, 1988, and assigned to the assignee of this application, discloses a transom mounted stern drive unit in which the position of the propeller may be adjusted vertically with respect to the transom. The apparatus allows the drive shaft to be maintained in a fixed position between the engine and the drive unit, but requires, as a result, a somewhat complex mechanical linkage to move the lower propeller unit vertically within the drive unit housing. U.S. patent application Ser. No. 241,615, entitled "Marine Propulsion System," filed Sept. 8, 1988, and also assigned to the assignee of this application, discloses a stern drive propulsion system including a transversely mounted engine and means for transferring power from the engine to the drive unit to accommodate vibrational engine movement and isolate the drive unit from the effects of such movement. The preferred embodiment of the power transmission means is a chain or belt drive from a horizontal engine crankshaft extension to a horizontal jackshaft in the drive unit. The drive unit is adapted to be pivoted about the jackshaft for trimming, but direct vertical movement of the drive unit is precluded.